Rafter Ties

[jimtheengineer10]

Attached is a picture that the homeowner had in mind.

Question 1:
My question is if a ridge beam is not installed then the rafter ties need to be installed near the bottom of the rafter and not in the top portion right?

Question 2:
Another option I was thinking of was installing a 2x4 from the rafter back to the 2x4 stud wall? If this was done could a regular ridge board be installed with collar ties in the top portion?

Thanks for the help.

 

[BAretired]

It makes even less sense now than it made before. What is left of the 8x8 beam after the joist pockets have been cut? Have you checked the capacity of the joists and beams for floor loading?

It would be more sensible to use 2x8 joists on top of the beams to avoid notching or alternatively, to use joist hangers and flush framing.

I doubt whether an 8x8 beam is adequate and, in any event it is not an economic size for a beam. The lap connection over the central column will tend to promote cracking in one of the beams and the notched connection to the exterior column is a poor detail.

The 2x4 diagonal brace fastened to rafters @ 4'-0" centers makes no sense at all with the framing system proposed. If you don't see this jimtheengineer10, I think you should be working under the supervision of a more experienced engineer.




BA

 

[jimtheengineer10]

BAretired,
I was skeptical of the plans and that is why I am asking the questions before I take on the project. The owner says he has built something just like this before and that it is still standing. Due to this he thinks he should be able to build the exact same thing even if engineering calcs show otherwise.

I think I will talk to the owner and recommend the following:
- install an lvl ridge beam and a couple posts on the second floor
- use 2x8 joists to sit on top of the beams instead of the 4x6 joists
- use hangers to connect the 8x8 beams to the posts

Would you recommend using hangers on each side of the post to support the two beams instead of the lap connection or is there a better option?

Thanks for all the help.

 

[BAretired]

Clients who have built it before and it is still standing are the hardest to deal with. I always tell them that the design must be in accordance with the code or I won't get involved.

My preference would be to butt the beams together at the middle of the column. A two span continuous beam is another option, but it may be difficult to buy one that long. In either case, I would use a suitable post to beam attachment as made by Simpson Strong Tie or similar.

The attachment to the exterior column should be a suitable hanger if the column is continuous as shown, but it might be easier to cut the column off at the underside of beam and let the beam run through. The upper length of column can easily be braced back to the beam.

BA

 

[msquared48]

To me, this looks like timber frame construction, post and beam. From everything I have seen over the years, ridge beams are usually employed, not collar ties. The loft floor joists connections are just not designed to take the lateral kick of collar ties and hide the connection.

I have seen hammer trusses employed, but that's an entirely different animal.

I am not saying that is cannot be done, but it is definitely not the norm.

Mike McCann
MMC Engineering

 

[BAretired]

@Mike: Probably the owner doesn't want posts at 10' centers on the second floor which he would need if using a ridge beam.

@jim: Why is the owner using 8x8 posts on the North and South walls? It would make more sense to span the second floor joists perpendicular to the ridge. They would bear on two exterior walls and a beam in the middle with a ten foot span between columns.

The roof rafters could be supported on stub walls bearing on second floor joists and rim boards. Ties at 4' centers could be provided as originally described in your earlier post.

BA

 

[jimtheengineer10]

Thanks for all the help with this. I decided to give the project to an architect who has done quite a few of these.